Technical Field
The present invention generally relates to a system to detect a level of paper in a paper supply available for printing in a printing device. More specifically, the level of paper in the supply that has been used or is remaining is measured in a continuous manner.
Description of the Prior Art
In a printing device using paper supplied from a paper supply, printing is carried out by successively feeding the paper supply to a printing position. When one printing job is finished, the used paper is subjected to cutting and/or separation from the paper supply. The size of a print image on the used paper may respectively differ for each print job. Accordingly, a shortage in a remaining amount of the paper supply may occur for a successive print job, causing a print interrupt.
To prevent interruption in the operation of the printing device due to no paper available for printing, it is known to use a detector to sense a low paper condition. One solution is to employ an encoder to measure the cumulative length of paper available for printing. Another solution uses a detecting arm which loses contact with an exterior circumferential surface of the paper roll when the paper roll reaches a “near end” state. Some known solutions provide the printing device with a signal indicative of the paper level. In response to the signal, the printing device indicates the low paper level condition to a user through a light emitting diode or a similar illumination device.
Known solutions detect only arbitrarily-defined paper “low” conditions and provide only a few discrete states of paper level, such as “Full,” “Near Empty,” and “Empty.” These solutions fail to indicate precise levels of paper during printing process and are limited to detecting a predefined number of discrete states of paper level. The transition from one state to another may be unexpected and sudden. In addition, most of the solutions are highly dependent on electronics. Paper level cannot be measured once electrical power is cut off. Accordingly, there is a need for an accurate measurement of a paper supply.